I. Field of the Invention
This invention relates to wireless communication systems and more particularly to a scalable radio platform that enables users of different wireless systems to communicate with each other.
II. Description of the Related Art
Wireless communications has experienced a tremendous growth in the past few years. As a result, there is an ever increasing demand by users to use these systems to convey not only voice signals, but also data signals and video signals. Several wireless communication systems have emerged as accepted standards in various parts of the world. Some of the major wireless communication systems include the Advanced Mobile Phone Service (AMPS), Personal Communication Services (PCS), GSM (Group Speciale Mobile), the High Performance Radio Local Area Network (HIPERLAN) and its U.S. equivalent, Unlicensed National Information Structure (U-NII) systems. Some of these systems are analog systems while others are digital. That is, some of these systems use analog modulation techniques while others use digital modulation techniques. Also, these systems allow their subscribers to access their equipment in different manners. Some systems use Frequency Division Multiple Access (FDMA) schemes while others use Time Division Multiple Access (TDMA) schemes, Code Division Multiple Access (CDMA) or F/TDMA (combination of FDMA and TDMA) schemes.
In addition to having incompatible parameters such as access schemes and modulation techniques, these systems have incompatible bandwidths, frequencies of operation, information transfer rate, and protocols. These are some of the parameters, known as system parameters, which define precisely how subscribers initiate communication, convey information to each other and terminate communication. Therefore, there are barriers for the communication between users of different wireless systems because of incompatible system parameters. With the advent of the Internet, subscribers of communication systems expect and require to have global communication capabilities regardless of their physical location or their particular service provider. Users of wireless communication systems have the same expectations and needs.
Furthermore, new frequency spectrum allocations are being created to satisfy the increasing demand for wireless services. As a result, system parameters (e.g., bandwidth, frequency of operation, transfer rate) are in a state of flux. Consequently, system providers at their great expense, often have to change or modify their system equipment to comply with these changing parameters. Also, factors such as sudden increases in subscriber usage or changing radio signal propagation conditions may effect the performance of the system. Thus, there is also a need by system providers to alter some of their system parameters (e.g., increase or reduce bandwidth, decrease transfer rate to reduce bit error rate) on an as needed basis in order to adapt their system to changing system conditions allowing them to operate their system more efficiently.
FIG. 1 depicts a typical wireless system. FIG. 1 shows a system level diagram of a typical digital cellular wireless system that uses a CDMA scheme. Message Switching Center (MSC) 6 communicates with the Public Switched Telephone Network (PSTN) 2 over bidirectional line 4. MSC 6 communicates with Cell Sites (CS) 12 located in each cell 14 via communication links 8. Each cell 14 is depicted as a hexagon which is a symbolic representation of the geographic terrain or physical area that is being served by a cell site. The cell can be represented with the use of other geometric shapes. Within each cell 14 are a plurality of mobile users 10 who communicate with each other, with users of other cells and with users within PSTN 2. Cell sites 12 communicate with mobile users 10 within each cell via wireless communication links 16. The Cell sites 12 typically contain (among other devices) a communication controller (not shown) that transmits, processes and/or receives information signals from either the users of the system, the MSC or other system equipment. User information signals are typically in the form of analog or digital voice signals, video signals or digital data signals. The system information signals are similarly represented and are used by the system equipment to monitor, control and operate the overall system. Wireless communication links 16 actually comprise two channels (not shown). One channel, commonly referred to as the system channel, is used to convey system information signals between mobile users 10 and cell sites 14. The other channel, commonly referred to as the traffic channel, is used to convey user information signals between the mobile users 10 and cell sites 14. The system is designed so that only mobile users who have subscribed to the system and who are located within one of the cells can use the system.